cc2538: spi: Do not call SPI_WAITFOREORx() at end of init

If the SSI has never been used and spi_init() is called, then the SSI receive
FIFO is empty and remains so, so calling SPI_WAITFOREORx() at the end of
spi_init() waits endlessly for SSI_SR.RNE to be set. Hence, this call must be
removed in order to avoid a deadlock.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
cc2538: spi: Include spi-arch.h before dev/spi.h

spi-arch.h configures dev/spi.h, so it must be #included first. Luckily, this
mistake did not have any consequence here, but fix it in order to avoid possible
future issues.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Allow payload len to be larger than 256 bytes
Allow the 6lowpan code to handle packets larger than 256 bytes
Added the const keyword to IP address arguments that are not (and should not be) changed by the callee
Add access to LQI and RSSI to Contiki motes
Added the const keyword to functions that use the tcpip_set_outputfunc(), which now takes a const argument
Removed old, unused and empty example
Removed old unused jcreate platform examples
Removed old, unused and now surprisingly named example
Removed old esb examples
Removed old unused sys/ files
Removed old unused tcpdump.c code
Removed out-commented timetable code
Removed old unused timetable code
Removed old unused profile.h code
Merge pull request #54 from cmorty/contiki_mote_lqi_support

Add access to LQI and RSSI to Contiki motes
Merge pull request #436 from adamdunkels/push/cleanup-examples

A first cleanup of the examples/ directory
Merge pull request #435 from adamdunkels/push/cleanup-net

Removed old unused tcpdump.c code
Merge pull request #434 from adamdunkels/push/cleanup-sys

Remove old unused code from the core/sys/ directory